Generator size by appliance / sump pump
What size generator runs a sump pump
Sump pump, 1/2 hp: 1,050 W running plus 2,150 W more for a few seconds as it starts, so a generator needs at least 3,200 W of starting capacity to run it on its own. The smallest of the six portables this site covers that can do it is the Westinghouse iGen5000 (3,900 W running, 5,000 W peak).
A sump pump matters most in the storms that cause outages, and it starts without warning whenever the pit fills. The generator has to be able to absorb that start at any moment, on top of whatever else is running.
The horsepower is printed on the pump's label. EWEB lists both sizes; Generac lists the 1/2 hp pump at 2,150 W of additional starting watts and EWEB at 2,200 W, a gap that does not change which generators fit.
If the pump and the refrigerator happen to start at the same moment, both surges land together. The usual method, and this site's, adds only the single largest surge, which assumes starts are staggered.
The figures and where they come from
| Device | Source | Running W | Additional starting W | Starting need alone |
|---|---|---|---|---|
| Sump pump, 1/2 hp | Generac GP brochure (2023) | 1,050 | 2,150 | 3,200 |
| Sump pump, 1/2 hp | EWEB (2019) | 1,050 | 2,200 | 3,250 |
| Sump pump, 1/3 hp | EWEB (2019) | 800 | 1,300 | 2,100 |
Highlighted rows are the figures the calculator uses. Every table here prints additional starting watts: the surge on top of running watts.
Which portables can run it
| Generator | Running / peak W | Alone | With fridge, 6 LED bulbs, 2 chargers |
|---|---|---|---|
| Honda EU2200i | 1,800 / 2,200 | No | No |
| Honda EU3000iS | 2,800 / 3,000 | No | No |
| Westinghouse iGen5000 | 3,900 / 5,000 | Yes | Yes |
| Honda EU7000iS | 5,500 / 7,000 | Yes | Yes |
| Champion 201040 | 7,500 / 9,375 | Yes | Yes |
| Westinghouse WGen9500DF | 9,500 / 12,500 | Yes | Yes |
A generator fits when its running rating covers every running watt and its peak (or "max") rating covers the running total plus the single biggest starting surge. Adding the basics — a refrigerator (700 W running, 2,200 W to start), six 15 W LED bulbs and two phone chargers — raises the running load to 1,880 W and the starting need to 4,080 W, because the refrigerator's surge is now the biggest one. The smallest portable here that covers that is the Westinghouse iGen5000.
On a standby generator
A home standby unit is rated in kilowatts and has no overload capacity: Generac's rating definition says "No overload capability is available for this rating." Using Generac's own formula — sum of running watts plus the highest single starting burst — the sump pump with the basics needs 4.1 kW. The smallest Guardian model that covers it on natural gas is the 10 kW, rated 9 kW on natural gas and 10 kW on propane, which leaves 4.9 kW of starting room for everything else. Whole-home lists are on the standby generator pages.
Sump pump, 1/3 hp
The smaller size needs 800 W running and 1,300 W more to start, 2,100 W in all; the Honda EU2200i is the smallest portable here that starts it alone. With the basics it needs 3,830 W to start.
Before running anything, read the carbon monoxide distance rules and how a transfer switch keeps power off the utility lines. Other appliances: refrigerator · well pump · furnace · window AC · central air · heat pump · space heater · water heater · washing machine · garage door opener · CPAP · oxygen concentrator.